Interesting - I had a partial fix locally for these issues, and I had also gone with the same approach of propagated instructions and ChangeType :) not exactly the same as yours, but similar.

Nice job! This SSA code is always a bit tricky to properly understand and review, but I don't see anything obviously wrong with it, and I can't argue with the number of bugs fixed :)

I assume that the added test cases already cover all the edge cases from the four bugs you're fixing. If that's not the case for an of them, please send a follow-up PR adding more test cases, verifying that they fail if you revert the fix. Good regression tests are absolutely crucial to make sure that our SSA code works like it's meant to.